1. Field of the Invention
The present invention relates to a machine tool in which a first headstock is fixed on a fixed bed at a longitudinal leftside end portion thereof as viewed from the machine front while a second headstock or tailstock is movably provided at a right-side end portion thereof, and a tool post is movably provided between the first and second headstocks.
2. Discussion of the Related Art
There has conventionally been provided a combined-machining lathe in which a first headstock is fixed on a fixed bed at a left-side end portion thereof as viewed from the machine front while a second headstock is provided at a right-side end portion thereof so as to be movable in a Z-axis direction. The upper and lower tool posts are provided between the two headstocks so as to be movable in the Z-axis direction. The lower tool post is placed linearly on the same fixed bed as the first and second headstocks.
In this type of combined-machining lathe, a workpiece set on the first headstock is machined by the lower tool post, while a workpiece set on the second headstock is machined by the upper tool post.
The lower tool post is structured so that a turret with a plurality of tools set thereon is rotationally indexably mounted on the tool post body. The turret is generally placed on the first headstock side of the tool post body.
The prior art combined-machining lathe described above adopts a structure that the lower tool post is placed linearly between the first and second headstocks on the fixed bed. This placement relationship means that the tool post body and the second headstock are likely to interfere therewith. Thus, there is a need for adopting a structure that avoids their interference.
For avoidance of such interference between the tool post body and the second headstock, it could be conceived to increase the distance therebetween. However, this would cause the fixed bed to become longer, which leads to a problem that the whole machine would be larger.
It could also be conceived to make the spindle portion of the second headstock largely overhang from the base portion toward the tool post side so as to avoid the interference with the tool post body. However, making the spindle portion of the second headstock overhang would cause the second headstock to decrease in structural support rigidity, which may, in some cases, lead to a decrease in machining accuracy.
The present invention has been accomplished by considering these circumstances in the prior art.
An object of the present invention is to provide a machine tool which can avoid interference between the tool post body and the second headstock without causing any increase in size of the whole machine or any decrease in the structural support rigidity.
In order to achieve the above object, in a first aspect of the present invention, there is provided a machine tool comprising: a first headstock fixed on a fixed bed; at least one of a tailstock and a second headstock is movably disposed on the fixed bed so as to be movable along the fixed bed; and a tool post body for rotationally supporting a turret having a plurality of tools set thereon, the tool post body being movably disposed between the first headstock and the at least one of a tailstock and a second headstock, wherein the turret is placed on one side of the tool post body that is closer to the at least one of a tailstock and a second headstock, and the first headstock has a recessed portion that is dimensioned to accommodate the tool post body therein.
In a second aspect of the invention, there is provided a machine tool as described according to the first aspect, wherein the first headstock comprises a base portion fixed to the fixed bed, and a spindle portion for supporting a spindle, the spindle portion including an overhanging portion that extends toward the at least one of a tailstock and a second headstock, the overhanging portion being connected to the fixed bed by a leg portion, and wherein the recessed portion is defined by the overhanging portion, the base portion and the leg portion.
In a third aspect of the invention, there is provided a machine tool as described according to the first or second aspect, wherein the base portion of the first headstock is formed so as to extend from an upper edge of a sloped surface to a lower edge of the sloped surface.
With the machine tool according to the present invention, since the turret is placed on one side of the tool post body closer to the tailstock (or the like such as a second headstock), interference between the tool post body and the tailstock (or the like) can be avoided without making the tailstock (or the like) overhang, thereby avoiding a decrease in the structural support rigidity involved in making the tailstock (or the like) overhang. This also results in preventing a decrease in the machining accuracy.
Also, since an accommodating portion into which the tool post body is allowed to enter is formed in the first headstock, the machining of the workpiece can be carried out while the tool post body is accommodated in the accommodating portion. Thus, while the turret is placed on the side closer to the tailstock (or the like), the workpiece can be machined with the cutting tool of the turret without increasing the size of the fixed bed and therefore the size of the whole machine can be maintained.
In the second aspect of the invention, since an accommodating or recessed portion is formed by making the spindle portion of the first headstock overhang from the base portion toward the tailstock (or the like) and by fixing this overhanging portion to the fixed bed with the leg portion, a decrease in the structural support rigidity can be avoided.
In the third aspect of the invention, since the base portion of the first headstock is formed so as to extend from an upper edge of a sloped surface to a lower edge of the sloped surface, a decrease in the structural support rigidity in making the spindle portion overhang can also be avoided in this respect.